The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Air is drawn into an engine through an intake manifold. A throttle valve may control airflow into some types of engines, such as spark-ignition engines. In other types of engines, such as compression-ignition engines, a throttle valve may be omitted. The air mixes with fuel from one or more fuel injectors to form an air/fuel mixture. The air/fuel mixture is combusted within one or more cylinders of the engine. Combustion of the air/fuel mixture generates torque.
Exhaust resulting from the combustion of the air/fuel mixture is expelled from the cylinders to an exhaust system. The exhaust may include particulate matter (PM) and gas. The exhaust gas includes nitrogen oxides (NOx), such as nitrogen oxide (NO) and nitrogen dioxide (NO2). A treatment system reduces NOx and PM in the exhaust.
For example, the exhaust may flow from the engine to an oxidation catalyst (OC). The OC removes hydrocarbons and/or carbon oxides from the exhaust. The exhaust may flow from the OC to a selective catalytic reduction (SCR) catalyst. A dosing agent injector injects a dosing agent into the exhaust stream, upstream of the SCR catalyst. Ammonia (NH3) provided by the dosing agent is absorbed by the SCR catalyst. Ammonia reacts with NOx in the exhaust passing the SCR catalyst. The exhaust may flow from the SCR catalyst to a particulate filter that filters particulate from the exhaust passing through the particulate filter.